system-wall-clock-ms.cc

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/*
 * Copyright (c) 2005 INRIA
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation;
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 * Author: Mathieu Lacage <mathieu.lacage.inria.fr>
 */
 
#include "system-wall-clock-ms.h"
 
#include "log.h"
 
#include <chrono>
 
namespace ns3
{
 
NS_LOG_COMPONENT_DEFINE("SystemWallClockMs");
 
class SystemWallClockMsPrivate
{
  public:
    void Start();
    int64_t End();
    int64_t GetElapsedReal() const;
    int64_t GetElapsedUser() const;
    int64_t GetElapsedSystem() const;
 
  private:
    std::chrono::system_clock::time_point m_startTime; 
    int64_t m_elapsedReal;                             
    int64_t m_elapsedUser;                             
    int64_t m_elapsedSystem;                           
};
 
void
SystemWallClockMsPrivate::Start()
{
    NS_LOG_FUNCTION(this);
    m_startTime = std::chrono::system_clock::now();
}
 
int64_t
SystemWallClockMsPrivate::End()
{
    //
    // We need to return the number of milliseconds that have elapsed in some
    // reasonably portable way.  The underlying function that we will use returns
    // a number of elapsed ticks.  We can look up the number of ticks per second
    // from the system configuration.
    //
    // Conceptually, we need to find the number of elapsed clock ticks and then
    // multiply the result by the milliseconds per clock tick (or just as easily
    // divide by clock ticks per millisecond).  Integer dividing by clock ticks
    // per millisecond is bad since this number is fractional on most machines
    // and would result in divide by zero errors due to integer rounding.
    //
    // Multiplying by milliseconds per clock tick works up to a clock resolution
    // of 1000 ticks per second.  If we go  past this point, we begin to get zero
    // elapsed times when millisecondsPerTick becomes fractional and another
    // rounding error appears.
    //
    // So rounding errors using integers can bite you from two direction.  Since
    // all of our targets have math coprocessors, why not just use doubles
    // internally?  Works fine, lasts a long time.
    //
    // If millisecondsPerTick becomes fractional, and an elapsed time greater than
    // a millisecond is measured, the function will work as expected.  If an elapsed
    // time is measured that turns out to be less than a millisecond, we'll just
    // return zero which would, I think, also will be expected.
    //
    NS_LOG_FUNCTION(this);
 
    auto endTime = std::chrono::system_clock::now();
 
    std::chrono::duration<double> elapsed_seconds = endTime - m_startTime;
    m_elapsedReal = std::chrono::duration_cast<std::chrono::milliseconds>(elapsed_seconds).count();
 
    //
    // Nothing like this in MinGW, for example.
    //
    m_elapsedUser = 0;
    m_elapsedSystem = 0;
 
    return m_elapsedReal;
}
 
int64_t
SystemWallClockMsPrivate::GetElapsedReal() const
{
    NS_LOG_FUNCTION(this);
    return m_elapsedReal;
}
 
int64_t
SystemWallClockMsPrivate::GetElapsedUser() const
{
    NS_LOG_FUNCTION(this);
    return m_elapsedUser;
}
 
int64_t
SystemWallClockMsPrivate::GetElapsedSystem() const
{
    NS_LOG_FUNCTION(this);
    return m_elapsedSystem;
}
 
SystemWallClockMs::SystemWallClockMs()
    : m_priv(new SystemWallClockMsPrivate())
{
    NS_LOG_FUNCTION(this);
}
 
SystemWallClockMs::~SystemWallClockMs()
{
    NS_LOG_FUNCTION(this);
    delete m_priv;
    m_priv = nullptr;
}
 
void
SystemWallClockMs::Start()
{
    NS_LOG_FUNCTION(this);
    m_priv->Start();
}
 
int64_t
SystemWallClockMs::End()
{
    NS_LOG_FUNCTION(this);
    return m_priv->End();
}
 
int64_t
SystemWallClockMs::GetElapsedReal() const
{
    NS_LOG_FUNCTION(this);
    return m_priv->GetElapsedReal();
}
 
int64_t
SystemWallClockMs::GetElapsedUser() const
{
    NS_LOG_FUNCTION(this);
    return m_priv->GetElapsedUser();
}
 
int64_t
SystemWallClockMs::GetElapsedSystem() const
{
    NS_LOG_FUNCTION(this);
    return m_priv->GetElapsedSystem();
}
 
} // namespace ns3